<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box1 {
            width: 300px;
            height: 300px;
            background-color: pink;
            color: #fff;
            font-size: 30px;
        }

        .box2 {
            width: 300pt;
            height: 300pt;
            background-color: blue;
            color: #fff;
            font-size: 30px;


        }

        .box3 {
            width: 210mm;
            height: 300pt;
            background-color: red;
            color: #fff;
            font-size: 30px;

        }

        .box4 {
            height: 500px;
            border: 1px solid red;
            width: 500px;
            background: yellow;

        }
    </style>
</head>

<body>
    <!-- <div class="box1">box盒子1</div>
    <div class="box2">box盒子2</div>
    <div class="box3">box盒子3</div> -->
    <div class="box4"></div>

</body>

</html>